Introduce Wikia API methods

[macbre]

Docs: http://www.wikia.com/api/v1

// @see http://poznan.wikia.com/api/v1/Mercury/WikiVariables
client.wikia.getWikiVariables(function(err, vars) {
  console.log(vars.theme['color-links']); // #006cb0
  console.log(vars.wikiCategories); // ["travel"]
});

// @see http://poznan.wikia.com/api/v1/User/Details?ids=119245&size=50
client.wikia.getUser(userId, function(err, function(err, user) {
  console.log(user.avatar);
  console.log(user.numberofedits);
});

// @see http://poznan.wikia.com/api/v1/User/Details?ids=1,119245&size=50
// Maximum size of id list is 100.
client.wikia.getUsers([user1Id, user2Id], function(err, function(err, users) {
  console.log(users[0].avatar);
  console.log(users[0].numberofedits);

  console.log(users[1].avatar);
  console.log(users[1].numberofedits);
});